Norethindrone can cause delayed or absence of menstrual blood flow. It has also been associated with weight gain. I would like to tell that ejaculation isn t necessary for fertilisation always. Some times pre ejaculatory fluids contains sperm that can be enough for conception. If you are taking norethindrone properly, then chances are very less of pregnancy even if there is an ejaculation. But as you have failed to mention about the exact timing of intercourse, I would suggest a pregnancy test if it was when you had made switch over or if you were not taking the pills regularly at that time - you have to take the pill at the same time everyday with less than 3 hours difference in timings.